In recent years, power generating systems using renewable energy have been drawing attention. As one of such power generating systems, a wind power generating system has been known which converts rotational energy of a wind mill into electric energy using a power generator. Moreover, recently, a wind-powered thermal power generating system has been proposed in which rotational energy of a wind mill is converted into heat energy by a heat generator employing heat generation through induction heating (eddy current) and the heat is converted into electric energy (for example, see Japanese Patent Laying-Open No. 2011-102576 (Patent Document 1) and Japanese Patent Laying-Open No. 2012-43728 (Patent Document 2)).
Further, for example, Japanese Patent Laying-Open No. 2003-120505 (Patent Document 3) and Japanese Patent Laying-Open No. 2004-63930 (Patent Document 4) propose a technique of improving power generation efficiency and a technique of effectively utilizing generated electric power in power generating systems employing renewable energy. Patent Document 3 proposes a technique of improving efficiency of a wind power generating device by driving a turbine using exhaust heat resulting from loss of a power generator coupled to a wind mill via a shaft and by recovering electric power as generated electric power from the power generator coupled to the turbine via the shaft in the wind power generating device. On the other hand, Patent Document 4 proposes a technique of effectively utilizing generated electric power as heat energy in a power generating system employing natural energy, in the following manner: an excess of electric power generated by power generating means (photovoltaic power generation or wind power generation) is converted into heat by an thermoelectric body and the heat is accumulated in heat accumulating means (electric water heater).